This thread caught my attention. I've been having the same issue with an Ellis Mountain 6000 liner and case. I gladly share my experience.
The EM 6000 case is a 76mm case for the M1000 load (too bad EM motors are going into extinction).
The phenolic liner was greased during assembly and the flight was nominal. We lost the rocket during recovery and it was a few months before someone found the rocket at the launch site. We immediately found the liner stuck in the case.
We used a 1.5" Oak dowel with sharp angle cut on one end and a rubber mallet to break out the phenolic. That worked about 1 foot into each end. The center part of the liner would not chip out.
Be careful using the forward closure and a large dowel to beat/push the liner out (with O-rings in place). We discovered the forward closure was damaging the interior wall of the case so I stopped that.
We tried putting the case in the freezer, but that did not work.
We tried leaving the case out in the Arizona summer sun to heat it up, but that did not work either.
We tried a propane torch to heat the case, but that did not work either.
We tried a heat gun, but hat did not work either.
We tried all manner of solvents, but that did not work either
I'm not giving up on this case as it will make a nice EX case even though there will be no more EM reloads soon.
One thing we have not tried, but may be a near last resort it taking it to an auto mechanic shop that has a vat for "boiling" engine blocks. What ever that solution is, it takes off gasket material which as been sealed and torqued on. That might work. I'll find out what that solution is and check with motor manufacturers first.